SummaryMannose-binding lectin (MBL) is a component of innate immunity and thus particularly important in neonates in whom adaptive immunity is not yet completely developed. Promoter polymorphisms and structural exon-1 mutations in the MBL2 gene cause reduced or deficient MBL plasma concentrations. The aim of our study was to determine the prevalence of MBL deficiency in neonates admitted to the neonatal intensive care unit (NICU). Eighty-five NICU patients (69 premature) were included in the study. We measured MBL concentrations in umbilical cord and neonatal blood within 24 h after birth by ELISA technique. MBL2 genotypes ( n = = = = 67) were determined by Taqman analysis. MBL concentrations were measured longitudinally during three weeks in 26 premature neonates. The association between pre-and intra-partum clinical data and MBL concentrations was investigated. At birth, 29 (42%) premature and six (38%) term neonates had MBL plasma concentrations ≤ ≤ ≤ ≤ 0·7 µ µ µ µ g/ml which was regarded as deficient. Twenty-one (38%) premature and four (36%) term neonates had variant MBL2 haplotypes, corresponding to exon-1 mutations and the LXPA haplotype. MBL concentrations increased over time in neonates with wild-type MBL2 haplotypes, but not in neonates with variant haplotypes. Low MBL plasma concentrations were related to lower gestational age and variant MBL2 haplotypes. Umbilical cord and neonatal MBL plasma concentrations appeared to be similar. In conclusion, almost half of our NICU patients, especially the premature ones, were MBLdeficient at birth. These infants may be at increased risk of neonatal infections. MBL concentration can reliably be measured in umbilical cord blood and it is positively correlated with gestational and postnatal age.

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The uptake and subsequent killing of Salmonella enterica serovar Typhimurium by human neutrophils was studied. In particular, two pattern recognition receptors, complement receptor 3 (CR3) and Toll-like receptor 4 (TLR4), were found to be essential for the efficient uptake and activation, respectively, of the NADPH oxidase. The uptake of Salmonella was almost completely inhibited by various monoclonal antibodies against CR3, and neutrophils from a patient with leukocyte adhesion deficiency type 1, which lack CR3, showed almost no uptake of Salmonella. A lipopolysaccharide (LPS) mutant strain of Salmonella was used to show that the expression of full-length, wild-type, or so-called smooth LPS is important for the efficient killing of intracellular Salmonella. Infection with wild-type-LPS-expressing Salmonella resulted in the generation of reactive oxygen species (ROS) in TLR4-decorated, Salmonella-containing vacuoles, whereas ROS were not induced by an LPS mutant strain. In addition, the recognition of Salmonella by neutrophils, leading to ROS production, was shown to be intracellular, as determined by priming experiments with intact bacteria under conditions where the bacterium is not taken up. Finally, the generation of ROS in the wild-type-Salmonella-infected neutrophils was largely inhibited by the action of a TLR4-blocking, cell-permeable peptide, showing that signaling by this receptor from the Salmonella-containing vacuole is essential for the activation of the NADPH oxidase. In sum, our data identify the sequential recognition of unopsonized Salmonella strains by CR3 and TLR4 as essential events in the efficient uptake and killing of this intracellular pathogen.